Emission testing circuit for color cathode ray tubes

ABSTRACT

The emission of the various electron guns of a color cathode ray tube are measured and indicated by a time sharing multiplexing technique where emission generating voltages are fed to the electrodes of the various electron guns in rapidly repeated sequence and the degree of emission thereof is displayed simultaneously on the faces of current meters responsive to average current flow. Such a technique permits simultaneous display of emission current for in-line cathode ray tubes having commonly connected control and/or accelerator electrodes, where individually adjustable spot cut-off voltages are sequentially connected to the set of commonly connected electrodes involved in synchronism at any given instant with the connections of the cathode electrode thereto which is to be assigned to the adjustable voltage involved.

BACKGROUND OF INVENTION

This invention relates to electron gun emission testing equipment forcolor cathode ray tubes.

Properly operating electron guns of a color cathode ray tube shouldoperate at adequate individual and relative emission levels. Theelectron guns must operate at proper relative emission levels to ensurea proper gray scale for a black and white picture producing video signalwhich would otherwise produce a colored tint if the relative emissionstrengths of the electron guns do not fall within an acceptable range ofvalues. To this end the ratio between the highest and lowest emittingelectron gun of a color cathode ray tube under voltage conditionsproducing a bright white indication must not be greater than 1.5 to passthe relative emission test under present standards.

In carrying out an emission test, commonly a fixed predeterminednegative bias voltage is first applied between each control electrodeand associated cathode electrode and an adjustable positive voltage isapplied between each accelerator electrode and the associated cathodeelectrode and adjusted to a value so current flow between the cathodeand accelerator electrodes indicated on a current meter just begins toflow, to produce what is called a spot cutoff emission level. Thevarious electron guns generally require different positive voltagelevels between the accelerator and cathode electrodes to produce a spotemission cutoff level. (Negative voltages applied between the controland cathode electrodes can be the individually adjustable spot emissioncutoff obtaining voltages, but this is not a convenient way to test theemission current.) The voltage on each control electrode is thenswitched to a value like chassis ground, which does not affect thepreviously adjusted accelerator to cathode voltage, to provide a highemission level which would produce a bright white intensity on the faceof the cathode ray tube under normal operating conditions. (Underemission test conditions, there is no voltage applied to the screen ofthe cathode ray tube.) The control and accelerator electrode voltagesare generally fed to the electron guns by manually operable switcheswhich feed the voltages involved to the electron guns in a sequenceselected by the operator. The operator notes the relative maximumemission values during the various measurements and computes the ratioof the emission levels of the highest and lowest emitting guns to see ifthe ratio exceeds an acceptable 1.5 to 1 value. In some emission testingequipment, a separate current meter is provided for each electron gun sothat the emission of all of the electron guns can be simultaneouslymeasured and indicated, making it an easier matter to determine theemission ratio of the electron guns. However, it is extremely difficultto design emission testing equipment which provides for simultaneousemission of all of the electron guns of all types of cathode ray tubes,including the recently developed "in-line" cathode ray tubes which havecommonly connected control and/or accelerator electrodes. The difficultyis caused by the problem of isolating the spot emission cutoff levelvoltage adjusting circuits connected between commonly connectedaccelerator electrodes and the individual cathodes of the electron gunsfrom the circuit which applies the initial negative reference voltageand the high intensity emission producing voltage between commonlyconnected control electrodes and the cathodes. (Obviously, the switchingof the commonly connected control electrodes from an initial referencelevel to a high intensity producing level should not effect the voltagescoupled between the commonly connected accelerator electrodes and theindividual cathode electrodes.)

In prior emission testing techniques which simultaneously measure theemission of all of the electron guns, the simultaneous flow of emissioncurrent from the three electron guns require relatively expensive wellregulated power supplies to avoid substantial variations of the voltagesfed to the accelerator electrodes when the control electrode voltage isswitched to a bright white intensity producing value. Anotherdisadvantage of prior emission measuring techniques in using sequentialmanual switching is the accompanying time delay involved for making thetest, including the waiting time for permitting the emission of anelectron gun to stabilize. Furthermore, less than desirable accuracy isachieved in obtaining relative emission measurements where the electronguns are made successively operable by manual switching techniques,since the separately operating electron guns do not duplicate or nearlyapproximate actual operating conditions and interactions betweenoperating electron guns and the possibility of intermittent operatingconditions are not then taken into account.

SUMMARY OF INVENTION

In accordance with one of the features of the present invention,substantially simultaneous measurement and indication of the emission ofthe electron guns of a color cathode ray tube is achieved in a uniqueway, by automatically switching the voltages between the cathode andaccelerator electrodes of the electron guns of a cathode ray tube sothat emission of the electron guns are sequentially established. In suchcase, the current flowing at any given instant is no greater than theemission required for a single electron gun, which reduces by a factorof at least 2/3 the current supplying requirements of a power supplywhich supplies only the emission current. Such a power supply can thusbe a relatively inexpensive regulated power supply. A separate currentmeter is preferably connected in the path of emission current flow foreach electron gun, each of which meters most advantageously has amovement which stabilizes at the average current value of the emissioncurrent involved, which preferably constitutes current pulsations at apulse repetition rate occurring many times per second. The presentinvention thus provides steady simultaneous indications of the flow ofemission current in all of the electron guns under conditions roughlyapproximating normal operating conditions when all electron guns areoperating at the same time.

Unlike the prior art, the emission test equipment of the inventionprovides a substantially simultaneous measurement and indication ofemission current for all types of cathode ray tubes including "in-line"cathode ray tubes where one or more of the electrodes of the separateelectron guns are connected together. In such case, the most severerequirement for the equipment is present where the individuallyadjustable spot emission cutoff level producing voltages are to beconnected to the commonly connected electrodes of the electron guns.This requirement poses no problem in this equipment because individuallyadjustable voltages to be coupled to the commonly connected electrodesare switched in synchronism with switching of the cathode electrodes ofthe electron guns. In using the emission test equipment of the preferredform of the invention designed for use with both in-line and non-in-linecathode ray tubes, the spot emission cutoff current levels of theelectron guns are obtained preferably by first connecting a referencenegative potential between the control and cathode electrodes of all ofthe electron guns, while the individually adjustable voltages,sequentially coupled between the accelerator and associated cathodeelectrodes preferably in rapid sequence, are adjusted to provideemission current levels at or slightly above their cutoff points. Then,the control electrode voltage is switched to a reference level, such aschassis ground, which establishes emission levels which would produce abright white indication on the face of a normal operating cathode raytube. A measurement of the large emission currents which flow throughthe various sequentially switched accelerator and cathode electrodecircuits then indicates the relative emission strengths of the threeelectron guns. If the emission level of any particular electron gun doesnot meet minimum requirements, a rejuvenation operation can be carriedout using known rejuvenation techniques.

The above and other advantages and features of the present inventionwill become more apparent by making reference to the specification tofollow with drawings and the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a preferred emission testing circuitincluding features of the present invention;

FIG. 2 is a fragmentary view of the face of the emission testing meterspreferably used in the exemplary form of the invention of FIG. 1;

FIGS. 3a, 3b, 3c, 3d, 3e, 3f, 3g, 3h and 3i respectively show on acommon time base waveforms of the voltages appearing in various portionsof the circuit in FIGS. 1 and 3; and

FIG. 4 is a view of the emission testing circuit of FIG. 1 with thesynchronizing circuit shown as a single block in FIG. 1 expanded intoexemplary functional components and the accelerator voltage adjustingcircuit shown partly in block form in FIG. 1 shown in exemplary circuitform.

DESCRIPTION OF EXEMPLARY EMBODIMENT OF INVENTION

In the drawing there is shown a cathode ray tube emission testingcircuit 1 which will generally constitute part of a greater overallcircuit (not shown) used to test the various characteristics of acathode ray tube. (For example, such equipment commonly performsleakage, life and focus tests in addition to a cathode rejuvenationoperation.) This overall circuitry is generally contained within ahousing identified by a dashed line 1a having various meters andcontrols on the outer face thereof, some of which are shown as part ofthe circuit 1 to be described. There is generally extending from thehousing of the cathode ray tube test and rejuvenating unit a cable 3having on the end thereof a socket connector 3a having generally up to12 socket terminals and associated conductors extending to various partsof the cathode ray tube test and rejuvenating circuitry necessary tocarry out the various test and rejuvenating operations involved. Sincethe plug connectors of cathode ray tubes of different design have avariety of configurations, it is necessary to provide a set of removableplug-in adapters, like unit 3b, which are each removably insertable intothe socket terminals of the socket connector 3a so that the plugconnectors like 2a at the bases of the various types of cathode raytubes can be connected to the appropriate points in the emission testingcircuit 1.

FIG. 1 shows a color cathode ray tube 2 having the usual three electronguns respectively including heater filaments 4a, 4b and 4c, surroundingcathode electrodes 6a, 6b and 6c with apertures aligned with the ends ofthe associated cathode electrodes, control electrodes 8a, 8b and 8c withrespective apertures aligned with the apertures of the associatedcontrol electrodes, and accelerator electrodes 10a, 10b and 10c withtheir apertures aligned with the apertures of the associated controlelectrodes. The cathode ray tube 2 illustrated is of the "in-line" typewherein the various control electrodes 8a, 8b and 8c are electricallyconnected together and the accelerator electrodes 10a, 10b and 10c areelectrically connected together within the cathode ray tube.

The heater filaments 4a, 4b and 4c are shown connected in parallelwithin the cathode ray tube and connected through the various plug andsocket terminals of the plug connector 2a at the base of the cathode raytube, the adapter unit 3b and the cable socket connector 3a toconductors 12 and 14 extending to the output of a filament voltagesource shown in block form and identified by reference numeral 16. Thefilament voltage source 16 is shown connected by conductors 17 and 18 toconductors 19 and 20 extending from a conventional plug connector 22adapted to be plugged into an AC outlet socket. The filament voltagesource 16 may be a circuit including a manually operable control member16a for adjusting a variac or transformer tap-off connecting switch (notshown) for varying the magnitude of an AC voltage appearing on theconductors 12 and 14. A voltmeter 16 indicating the magnitude of thisvoltage is coupled across the conductors 12 and 14. The control member16a is adjusted so that the rated voltage of the cathode ray tubefilaments appears across the conductors 12 and 14 extending to theheater filaments of the selected cathode ray tube under test.

The cathode electrodes 6a, 6b and 6c are connected through the variousplug and socket terminals of the cathode ray tube plug connector 2a, theadapter unit 3b and the cable socket connector 3a to respectiveconductors 24a, 24b and 24c. The conductors 24a, 24b and 24c areconnected through respective emission current indicating meters 25a, 25band 25c, switch means 26a, 26b and 26c and a common switch means 27 tochassis ground 28.

The commonly connected control electrodes 8a, 8b and 8c are connectedthrough the plug and socket terminals of the cathode ray tube plugconnector 2a, adapter unit 3b and cable socket connector 3a to aconductor 29 connected to the wiper 30a of a manually operable switch30. The switch 30 is a function selector switch having a number ofstationary contacts of which stationary OFF contact 30b, SET contact 30cand TEST contact 30d are illustrated. The stationary OFF contact 30c isconnected to the wiper 31a of a voltage adjusting potentiometer 31 andthe TEST stationary contact 30d is connected to chassis ground. One endof the voltage adjusting potentiometer 31 is shown connected to chassisground and the other end is coupled by a conductor 32 to the negative DCvoltage terminal 33 of the DC voltage source 34 energized from AC inputconductors 19 and 20. The DC voltage source 32 may include variousrectifiers, transformers and the like for providing a desired negativevoltage with respect to chassis ground at the terminal 33. The wiper 31aof the potentiometer 31 is adjusted to a desired reference negativevoltage for carrying out the emission test on the particular cathode raytube involved. A voltmeter 36 is shown connected between the conductor29 and chassis ground to indicate the output voltage of thepotentiometer 31 fed to the control electrodes of the cathode ray tube2.

In the case where the cathode ray tube 2 is one wherein the controlelectrodes are separate rather than connected together within thecathode ray tube, these various control electrodes can be coupledthrough various plug connections on the base of the cathode ray tube, anadapter unit different from 3b shown in the drawing, and cable socketconnector 3a to the conductor 29. (The socket terminals of connector 3afor making these connections are shown in the drawing together withtheir associated conductors 29' and 29" connected to conductor 29. )Accordingly, when the wiper 30a is connected to the stationary SETcontact 30c, a selective negative control voltage is fed to the controlelectrodes of the cathode ray tube involved.

When the wiper 30a is connected to the TEST contact 30d, the wiper iscoupled to chassis ground which will feed reference chassis groundpotential to the control electrodes of the cathode ray tube, whichgenerally produces a bright white trace producing emission of theelectron guns involved.

The commonly connected accelerator electrodes 10a, 10b and 10c arecoupled through the various plug and socket terminals of the cathode raytube plug connector 2a, adapter unit 3b and the cable socket connector3a to conductor 35 extending to a circuit now to be described, which atany instant feeds one of three manually adjustable voltages to theaccelerator electrode to be associated with the electron gun which is tobe rendered operative at the instant involved. In the example of thepresent invention shown, automatically and in rapid fire cyclicallyrepeating sequence the various cathode emission circuits of the electronguns are rendered operative in synchronism with the feeding of threeindividually adjustable voltages to the commonly connected acceleratorelectrodes.

The cable socket connector 3a is adapted to be operative with cathoderay tubes having separate as well as commonly connected acceleratorelectrodes and, to this end, is provided with socket terminals andassociated conductors 35' and 35" which extend to the aforesaidconductor 35.

The adjustable voltage circuit now to be described obtains it energizingvoltage from a voltage terminal 37 of the DC voltage source 34. A bus 38is shown connected to the terminal 37, and a conductor 39 extends fromthis bus 38 to a synchronizing circuit 40 to be described in more detailhereinafter, which circuit is operative to generate various timing andcontrol voltage waveforms shown in FIGS. 3a through 3i. Suffice it tosay at this point, in the exemplary form of the invention beingdescribed, the synchronizing circuit produces preferably square positiveand/or negative going control pulses like pulses P1-P2-P3 andP1'-P2'-P3' shown in FIGS. 3b, 3c, 3d, 3e, 3f and 3g respectivelyoccurring during successive equal time segments t1, t2 and t3 (FIG. 3a)of a basic repeating time period T1. These control pulses are used asgate opening or switch closing control signals.

The synchronizing circuit 40 has three output terminals 40-1, 40-2 and40-3 at which positive going control pulses P1, P2 and P3 respectivelyappear at the relative timing shown in FIGS. 3b, 3c and 3d. Timingcontrol lines 43-1, 43-2 and 43-3 are respectively coupled to theaforementioned synchronizing circuit output terminals 40-1, 40-2 and40-3 and respectively extend to control input terminals 26a-1, 26b-2 and26c-3 of the aforementioned switch means 26a, 26b and 26c associatedwith the cathode circuits of the color cathode ray tube 2. The switchmeans 26a, 26b and 26c, which may be transistors, become closed by thecontrol pulses P1, P2 and P3 only for the duration thereof.

The synchronizing circuit 40 has a clock pulse output terminal 40-4 atwhich narrow clock pulses P4 as shown in FIG. 3a appear. The clockpulses P4 occur at the beginning of each of the time segments t1, t2 and53, etc. There are thus three clock pulses per period T1 during whichthe control pulses P1, P2 and P3 are sequentially fed to the threeelectron guns of the cathode ray tube 2. The clock pulses at the outputterminal 40-4 of the synchronizing circuit 40 are fed to a proportionalcontrol circuit 45 which initiates the generation of variable widthpules P5 shown in FIG. 3e. The pulses P5 have identical widths which areadjusted by a manually operable control member 46. The proportionalcontrol circuit 45 may be a one-shot multivibrator of conventionaldesign.

The variable pulse width output of the proportional control circuit 45appears at an output terminal 47 which is connected to a control line 48extending to the control terminal 49 of the switch means 27 connected incommon with the switch means 26a, 26b and 26c. Each pulse P5 from theoutput of the proportional control circuit 45 closes the switch means 27to couple chassis ground through the switch means 26a, 26b or 26c closedat the same time. It is thus apparent that by varying the width of thepulses P5, the duration during which electron gun emission current flowsproportionately varies. (This part of the circuit is a sole invention ofGus Rose and is the subject of a co-pending patent application which isbeing filed on the same date as the present application.) This featureof the circuit is utilized to providing an indication on the faces ofthe current meters 25a, 25b and 25c in a manner to be described, whichimmediately indicates whether or not the relative magnitudes of thehighest and lowest emitting electron guns fall within an acceptable 11/2to 1 ratio for reasons previously explained.

The circuit for supplying the positive voltage to the acceleratorelectrodes is uniquely a voltage regulator circuit coupled between thepositive bus 38 extending the DC voltage source 34 and theaforementioned conductor 35 which is coupled through the variousconnectors 3a, 3b and 2a to the accelerator electrodes 10a, 10b and 10c.This voltage regulator circuit provides three adjustable voltages whichare sequentially coupled to the conductor 35 in synchronism with theoperation of the switch means 26a, 26b and 26c, so that the appropriateadjustable voltage is applied to the selected gun in a manner to bedescribed. The DC voltage source 34 is the main source for DC current ofthe entire circuit shown and it would materially add to the cost of themanufacture of the test equipment if this DC voltage source would be aregulated DC voltage source. If the DC voltage source 34 is not aregulated voltage source, the output thereof can fluctuate withvariation in line voltage and with the current supplied therefrom. It isone of the unique features of the present invention to provide aseparate voltage regulator circuit for only the circuit supply voltageto the accelerator electrodes and which, in the preferred form of theinvention, is designed to operate for variations in emission currentflow from zero to the average current which flows between the cathodeand accelerator electrodes of the cathode ray tube during the sequentialswitching means of the different levels of output voltage of the voltageregulator circuit. (To produce simultaneous meter indications ofemission current flow if all electron guns were to be continuouslyoperative to supply such current flow, the current requirements for thevoltage regulator circuit now to be described would be three times thatnecessary when the electron guns are sequentially rendered operative, aspreviously explained.)

The voltage regulator circuit includes a voltage varying means 50connected between the positive bus 38 and the conductor 35 connectedwith the accelerator electrodes of the cathode ray tube 2. The voltagevarying means could be a power resistor where a shunt regulator circuitis utilized or a variable resistance device like a transistor where aseries regulator circuit is utilized. Associated with variable voltagemeans 50 is a control means 51 which, in accordance with well knownseries or shunt regulating techniques, responds to the output of asource of reference voltage 52 and a voltage derived from the voltage atthe output of the voltage varying means to provide a stabilized voltageon the conductor 35 independently of input voltage and current flowvariations over given limits. Thus, the source of reference voltage 52is shown connected to an input 51' of the control means 51 and a voltagederived from the output conductor 35 is coupled to the control means 51at an input terminal 51" thereof.

Three different manually adjustable voltages are most advantageouslysequentially fed to the input terminal 51" of the control means 51.These adjustable voltages are obtained in the most preferred form of theinvention in the manner illustrated. Thus, three circuit branches extendbetween the conductor 35 and chassis ground, which branches respectivelyinclude fixed resistors 55a, 55b and 55c in series with potentiometers57a, 57b and 57c. The wipers 57a', 57b' and 57c' of the potentiometers57a, 57b and 57c are respectively connected to the input terminal 51" ofthe control means 51 through isolating rectifiers 59a, 59b and 59c. Onlyone of the branch circuits is rendered operative at any given time tocouple voltage from the wiper of the associated potentiometer by aswitching circuit comprising switch means 60a, 60b and 60c. When closed,switch means 60a, 60b or 60c applies chassis ground to the junctionbetween the associated resistors 55a, 55b or 55c and the potentiometers57a, 57b or 57c. The switch means 60a, 60b and 60c can be closed by thefeeding of a positive control voltage through control input terminals60a', 60b' and 60c', the voltages being obtained respectively from theoutput of inverters 62a, 62b and 62c, whose inputs extend to the timinglines 43-1, 43-2 and 43-3 at which the positive pulses P1, P2 and P3 ofFIGS. 3b, 3c and 3d appear. The inverters 62a, 62b and 62c respectivelyinvert the positive going pulses P1, P2 and P3 to negative going pulsesP1', P2' and P3' shown in FIGS. 3e, 3f and 3g. These negative goingpulses decrease from a normal positive level to chassis ground. Thus, atany one time two of the switch means 60a, 60b and 60c are closed by thepositive portions of the waveform shown in FIGS. 3e, 3f and 3g, and oneof the switch means is opened by the presence of a negative going pulseP1', P2' or P3'. Switch means 60a, 60b and 60c are, accordingly, closedin sequence in synchronism with the closing of switch means 26a, 26b and26c which sequentially connects chassis ground potential to the cathodeelectrodes 6a, 6b and 6c of the cathode ray tube 2. With the orientationof the rectifiers 59a, 59b and 59c illustrated, the rectifiersassociated with the potentiometers which are being grounded by theclosure of the associated switch means 60a or 60b are back-biased intonon-conduction by the voltage coupled to input terminal 51' of thecontrol means 51 by the rectifier associated with one switch means whichremains open.

By varying the position of the wiper of any potentiometer, the voltageat the output of the voltage varying means 50 to which the conductor 35extends will vary proportionately, so that three different voltagelevels are established in sequence on the conductor 35 by the switchingsystem shown. FIG. 3i shows these three different voltage levels L1, L2and L3 which may be present on the conductor 35 in the time segmentsillustrated. If the voltage on the conductor 35 during a given timesegment t1, t2 and t3 tends to go up or down, in accordance withconventional voltage regulator action, the control means 51 will operatein a way which stabilizes the voltage on the conductor 35. Whether ornot an electron gun is operating properly is determined by themeasurement shown on the associated current meters 25a, 25b or 25cwhich, in turn, is directly related to the provision of a stable voltageon the conductor 35. To achieve such stability in the emission testingcircuits of the prior art, where all electron guns are simultaneouslycontinuously operative to provide simultaneous emission indications,required three expensive bleeder resistors or three series or shuntregulator circuits to provide the three separately adjustableaccelerator voltages. The three regulator circuits were not utilizedbecause of their prohibitive cost. The use of three bleeder resistors isrelatively costly, gives less than ideal voltage regulation and iswasteful of power. In the present invention, simultaneous indications ofemission current flow is obtained with the near ideal voltage regulationprovided by only a single series or shunt regulator circuit requiringrelatively little power and operating with only 1/3 of the currentrequirements of a circuit which must carry emission currentsimultaneously and continuously flowing in three electron guns, as inthe case of prior emission testing circuits providing simultaneousemission indications.

Before describing the manner in which the emission measuring circuit ofFIG. 1 is utilized, it would be helpful first to examine the face of anexemplary meter preferably utilized for each of the meters 25a, 25b and25c. Thus, as shown in FIG. 2, each of the meters 25a, 25b and 25c has ameter face 56 with an annular band divided into a BAD segment 56a (whichmay be colored red), a GOOD band segment 56b which may be colored green,and a TRACKING GOOD segment 56b' at the left corner portion of thesegment 56b. The segment 56b' may be colored for example, yellow or anyother color contrasting to the color of the segments 56a and 56b. Alongthe outer margin of the band segments 56a, 56b and 56c is a scale 58with scale markings and indicia indicating various values of emissioncurrent flow indicated by the position of a meter movement pointer 59movable over the face 56 of the meter.

To initially energize the circuit shown in FIG. 1, a master on-offmanually operable switch 61 may be provided on the housing 1a whichswitch when closed feeds power from the outlet plug conductors 19 and 20to the DC voltage source 34 and the filament source 16.

To make an emission test of the cathode ray tube 2, initially the wiper30a of the function switch 30 is moved to the stationary SET contact 30cwhich couples the output of the potentiometer 31 to all of the controlelectrodes 8a, 8b and 8c. The filament voltage adjusting control 16a isrotated until the voltmeter 16b indicates the presence of a properfilament voltage, and the control electrode potentiometer is adjusted toprovide the proper control electrode voltage on voltmeter 36 for thespot cutoff level adjustment operation (which voltage is commonly minus50 volts).

The various chassis ground and cathode connected switch means 26a, 26band 26c are rendered operative in a rapidly repeating sequence at a ratepreferably occurring as much as 20 times per second. The stepped voltagewaveform shown in FIG. 3i is fed to the voltage regulator circuit 54 insynchronism with the sequential closing of the switch means 26a, 26b and26c. Next, the control 46 of the proportional circuit 45 is adjusted toa given reference position which maximizes the duration of the pulses P5controlling the closing of the common switch means 27. A maximumduration of these pulses is, of course, no greater than the timesegments t1, t2 and t3 of FIG. 3a.

The accelerator voltage adjusting potentiometers 57a, 57b and 57c arethen adjusted so that the pointers 59 on the various current meters 25a,25b and 25c are located slightly above the zero marker on the scale 57,such as opposite the first division marker 57a, so that the emissiongenerated by the various electron guns are near the spot cutoff level.

The wiper 30a of the function control switch 30 is then moved to thestationary TEST contact 30d which applies chassis ground to the variouscontrol electrodes. This causes an appreciable emission of the variouselectron guns, if the emission capabilities of the electron guns aresatisfactory. If any of the pointers 59 of the meters 25a, 25b or 25c islocated in the BAD band segment 56a, this indicates poor emission and arejuvenation operation well known in the art can be carried out to seeif the electron gun involved can be rejuvenated.

If all of the electron guns show a satisfactory emission, the manuallyoperable control 46 of the proportional circuit 45 is adjusted todecrease proportionately the emission of the various electron guns to apoint where the pointer 59 associated with the electron gun havingmaximum emission is in alignment with a marker line 56c shown in FIG. 2opposite the scale marker 58b indicating an emission current of 0.75milliamps. If a pointer 59 of any of the other meters then falls belowthe TRACKING GOOD segment 56b, that is below the marker 58c on scale 58indicating a current of 0.5 milliamps in FIG. 2, this means that theacceptable 11/2 to 1 ratio of the emission between the highest andlowest emitting electron guns is not present.

While the specific circuit details of the various component parts of thecircuit FIG. 1 may vary widely, reference shall now be made to FIG. 4which shows additional details of the synchronizing circuit 40 and thevoltage regulator circuit. As shown in FIG. 3, the synchronizing circuit40 may include a clock pulse generator 40A which may be energized by aconductor 61 extending from the positive bus 38. As previouslyindicated, the output of the clock pulse generator 40A shown in FIG. 3ais fed by a line 44 to the proportional control circuit 45 which isillustrated as a one-shot multivibrator. The manually operable control46 of the proportional control circuit 45 is shown varying the value ofa potentiometer 46' circuit thereof (not shown) which varies the timeconstant of a capacitor charge circuit for controlling the duration ofthe pulse output of the one-shot multivibrator. The output of the clockpulse generator 40A is also fed by conductor 63 to a suitable timingpulse generator circuit which may be a step switch means 40B which couldbe a mechanical stepping switch, or more preferably an electronic stepswitch, like a self resetting ring counter. A ring counter may comprisea series of cascaded bistable circuits or stages which have outputs towhich the timing lines 43-1, 43-2 and 43-3 are respectively connected.Each of these stages has an output which is either a relatively highvoltage of a given polarity or a zero or ground potential voltage, andall stages but one at any given instant provides one or the other ofthese two possible output conditions. As each timing pulse is fed tosuch a ring counter, the stage which has a distinctively differentoutput condition is reset to the other output and the next stage is setto the distinctively different output condition. A reset circuitcomprising a differentiating network of a capacitor 66 and resistor 68is shown connected to an input 70 of the first stage of the ringcounter. Also, a DC input line 71 is shown connecting positive bus 38 tothe B plus input terminal 71' of the ring counter. The counter thusresets itself every three clock pulses fed to the input thereof, so thatthe clock pulses result in the generation of the pulses P1, P2 and P3shown in FIGS. 3b, 3c and 3d, where the distinctively different outputis a positive voltage like that shown for pulses P1, P2 or P3.

FIG. 4 shows timing lines 43-1, 43-2 and 43-3 respectively extending tothe base electrodes of NPN transistors 26a, 26b and 26c constituting theaforementioned correspondingly numbered switch means. The collectorelectrodes of the transistors 26a, 26b and 26c, respectively areconnected to the current meters 25a, 25b and 25c and the emitterelectrodes thereof are shown connected to the emitter electrode of anNPN transistor 27 constituting the aforesaid switch means 27 whoseemitter is connected to chassis ground and whose base electrode isconnected to the output of the aforementioned one-shot multivibrator 45.

FIG. 4 shows an exemplary series-type voltage regulator circuit forregulating the voltage fed to the conductor 35 extending to theaccelerator electrodes 10a, 10b and 10c of the cathode ray tube 2. Asthere shown, voltage varying means 50 in FIG. 1 is shown as an NPNtransistor 50 whose conduction is controlled by an NPN controltransistor 51 whose collector is connected to the base of transistor 50and whose emitter is connected to the cathode of a Zener diode 52 whoseanode is connected to chassis ground. A voltage-dropping resistor 52'extends between the cathode of the Zener diode 52 and the positive bus38 so a fixed reference voltage is established at the juncture betweenthe resistor 52' and the Zener diode 52. A resistor 50' extends betweenthe base of transistor 50 and bus 38. The base of the control transistor51 extends to the common outputs of the isolating rectifiers 59a, 59band 59c.

The aforementioned switch means 60a, 60b and 60c are shown in FIG. 4 asNPN transistors 60a, 60b and 60c. The emitters of these transistors areconnected to chassis ground, and the collectors thereof are connectedrespectively to the juncture between resistors 55a, 55b and 55c and thepotentiometers 57a, 57b and 57c. The bases of the transistors 60a, 60band 60c are respectively connected to the outputs of the aforementionedinverters 62a, 62b and 62c.

It can be seen that as a wiper 57a', 57b' or 57c' of any of thepotentiometers 57a, 57b or 57c is adjusted so that the wiper is movedtoward the output conductor 35, during the time that the potentiometerinvolved is effective in coupling a voltage through the associatedisolating diode the voltage on the base of control transistor 51 willbecome more positive, causing the collector current of the controltransistor 51 to increase, thereby by-passing more of the drive currentfrom the transistor 50. The transistor 50 will then act as a higherimpedance, dropping more voltage thereacross and dropping the voltage onthe conductor 35 during the time segment t1, t2 or t3 involved. As thewiper on the potentiometer is moved closer to chassis ground, theinverse of the operation of the regulator circuit will occur. The wipersof the various potentiometers thus set a control point for the output ofthe voltage regulator circuit, which will operate in a direction tostabilize the voltage on the conductor 35 due to increases or decreasesof voltage caused by variations in the output of the main DC voltagesource 34 or an increase in emission current flow through the voltageregulator circuit.

It is apparent that the present invention can provide simultaneousindications of emission current flow for all the electron guns of acolor cathode ray tube of the in-line or other types and in a manner andunder conditions which greatly reduce the current requirements of theregulated voltage source.

It should be understood that numerous modifications may be made in themost preferred forms of the invention described without deviating fromthe broader aspects of the invention.

We claim:
 1. In a circuit for testing the emission of the electron gunsof a color cathode ray tube and including heater filament, cathode,control and accelerator electrode connecting terminals to be connectedrespectively to the heater filament, cathode, control and acceleratorelectrodes of the respective electron guns of a color cathode ray tube,a source of heater current to be continuously connected to said heaterfilament connecting terminals for continuously energizing the heaterfilaments of the electron guns of the cathode ray tube under test, andvoltage source means to be connected between the cathode and one of theother electrodes of each electron gun for causing electron emissionwhich is an indication of the electron emitting capabilities thereof,the improvement comprising separate emission indicating means for eachelectron gun of the cathode ray tube to be tested, each emissionindicating means providing an indication as to whether or not thecurrent flow between the cathode and said other electrode of theassociated electron gun is at an adequate level, and switching means forsequentially connecting said voltage source means and emissionindicating means to said electron gun electrode connecting terminals forcyclically establishing in sequence the flow of emission current betweenthe cathode and said other electrodes of said various electron guns,whereby emission current flow occurs in only one electron gun at anygiven time segment of each switching cycle, while said emissionindicating means simultaneously indicate the emission produced by theelectron guns.
 2. The color cathode ray tube emission testing circuit ofclaim 1 wherein said voltage source means includes a regulated source ofvoltage where the output thereof is maintained substantially constant asthe current flow therefrom increases from near zero to an average leveloccurring during said sequential operation of said electron guns, andwherein the output thereof would materially reduce in value if currentflow therefrom would increase to an order of magnitude of three timesaid average level.
 3. The color cathode ray tube emission testingcircuit of claim 1 wherein said voltage source means includes separatelymanually adjustable means providing a selection of output voltages to berespectively coupled to its commonly connected electrodes of an"in-line" or other type of color cathode ray tube, said switching meanseffecting the sequential coupling of said output voltages respectivelyto said electrode connecting terminals to be connected to the commonlyconnected electrodes of said cathode ray tube and the coupling of saidcathode electrode connecting terminals to said voltage source means insynchronism with the coupling of the output voltage to the associatedtherewith to the commonly connected electrodes.
 4. The color cathode raytube emission testing circuit of claim 1 wherein said indicating meansindicate average current flow therethrough and said switching means forsequentially connecting said voltage source means and emissionindicating means to said electron gun electrode connecting terminalscyclically establishing in rapid firing sequence recurring many time persecond the flow of emission current between the cathode and acceleratorelectrodes of said various electron guns.
 5. The color cathode ray tubeemission testing circuit of claim 3 wherein said voltage source meansincludes a regulated source of voltage where the output thereof ismaintained substantially constanct as the current flow therefromincreases from near zero to an average level occurring during saidsequential operation of said electron guns, and wherein the outputthereof would materially reduce in value if current flow therefrom wouldincrease to an order of magnitude of 3 times said average level.
 6. Thecolor cathode ray tube emission testing circuit of claim 1 wherein saidvoltage source means includes separately manually adjustable meansproviding a selection of output voltages with respect to a referencepotential point to be respectively coupled to the commonly connectedelectrodes of an "in-line" or other type of color cathode ray tube, saidswitching means effecting the sequential coupling of said outputvoltages respectively to said electrode connecting terminals to beconnected to the commonly connected electrodes of said cathode ray tubeand the coupling of said cathode electrode connecting terminals to saidreference potential point in synchronism with the coupling of the outputvoltage to be associated therewith to the commonly connected electrodes.7. The color cathode ray tube emission testing circuit of claim 1wherein said switching means sequentially connects said voltage sourcemeans and emission indicating means in sequence between the acceleratorand cathode electrode connecting terminals associated with said electronguns.
 8. The color cathode ray tube emission testing circuit of claim 3wherein said switching means couples said voltage source means andindicating means sequentially between the accelerator and cathodeelectrode connecting terminals associated with said electron guns. 9.The color cathode ray tube emission testing circuit of claim 8 providedwith a source of adjustable negative voltage coupled between saidcontrol and cathode connecting terminals and means for selectivelyremoving said adjustable negative voltage from said cathode connectingand control electrode terminals and connecting said cathode and controlelectrode connecting terminals to a reference voltage which produces arelatively high intensity cathode emission in a normal operatingelectron gun.
 10. In a circuit for testing the emission of the electronguns of a color cathode ray tube and including heater filament, cathode,control and accelerator electrode connecting terminals to be connectedrespectively to the heater filament, cathode, control and acceleratorelectrodes of the respective electron guns of a color cathode ray tube,a source of heater current to be continuously connected to said heaterfilament connecting terminals for continuously energizing the heaterfilaments of the electron guns of the cathode ray tube under test, andvoltage source means to be connected between the cathode and one of theother electrodes of each electron gun for causing electron emissionwhich is an indication of the electron emitting capabilities thereof,the improvement comprising separate emission indicating means for eachelectron gun of the cathode ray tube to be tested, each emissionindicating means providing an indication as to whether or not thecurrent flow between the cathode and said other electrode of theassociated electron gun is at an adequate level; said voltage sourcemeans including a main source of unregulated voltage having outputterminals at which a DC voltage appears which can vary appreciably; anda voltage regulator circuit comprising voltage varying means to beconnected in series between one of said output terminals and saidcathode and said other electrode connecting terminals, a source ofreference voltage, adjusting means whose input is coupled to the outputof said voltage varying means for providing an output representing aselected proportion of the input voltage thereto, control meansresponsive to the output of a voltage adjusting means coupled with saidsource of reference voltage for operating said voltage varying means toprovide at the output thereof a voltage which is a function of thedifference between the output voltage of said voltage adjusting meansand said source of reference voltage for stabilizing the adjustedvoltage at the output of said voltage varying means with fluctuations ofvoltage or current from said main source of unregulated voltage, andswitching means for repeatedly sequentially coupling a different one ofthe outputs of said adjusting means to said control means in synchronismwith the repeatedly sequential connection of the regulated output ofsaid voltage regulator circuit between said cathode and said otherelectrode connecting terminals.
 11. The color cathode ray tube emissiontesting circuit of claim 10 wherein said switching means couples saidregulated output of said voltage varying means sequentially between theaccelerator and cathode electrode connecting terminals associated withsaid electron guns.
 12. The color cathode ray tube emission testingcircuit of claim 11 provided with a source of adjustable negativevoltage coupled between said control and cathode connecting terminals,and means for selectively removing said adjustable negative voltage forsaid cathode and control grid connecting terminals and connecting thesaid cathode and control electrode connecting terminals to a referencevoltage which produces a relatively high intensity cathode emission in anormal operating electron gun.